Federal emissions regulations mandate the reformulation of fuels, such as gasoline fuel, sold at pumps to reduce the content of toxic and ozone-forming compounds in vehicle emissions. For example, to reduce the emission of volatile organic compounds (VOC), fuels sold in southern areas (e.g., areas categorized under ASTM class B) may be required to have a lower Reid vapor pressure (RVP) as compared to fuels sold in northern areas (e.g., areas categorized under ASTM class C) during summer months. Specifically, the differences in climate between the two types of areas may require a corresponding difference in the gasoline fuel volatility to achieve the same emissions effect.
Conventional gasoline engine vehicles and hybrid electric vehicles (HEVs) usually consume fuel in a relatively short period of time. Therefore, such vehicles are typically running on the correct fuel grade specific to that region for that season. However, with the advent of Plug-in HEVs (PHEVs) wherein a person may keep charging the vehicle and running the vehicle primarily in the electric mode, a vehicle may be running on the wrong fuel grade for that season. For example, during a summer season, a PHEV may have a winter-grade fuel in the fuel tank due to frequent charging and reduced usage of gasoline over the winter months. Likewise, during a winter season, the PHEV may have a summer-grade fuel in the fuel tank during winter due to frequent charging and reduced usage of gasoline over the summer months. Due to differences, such as volatility difference, between the summer and winter-grade fuels, the winter-grade fuel when used in summer may negatively impact vehicle emissions, while the summer-grade fuel when used in winter may degrade engine cold-starts. Overall, vehicle performance and emissions are degraded.
Thus, in one example, some of the above issues may be at least partly addressed by a method of operating a vehicle including an engine and a motor comprising, adjusting an engine fuel injection amount based on a seasonal grade of fuel in a fuel tank of the vehicle relative to a season of vehicle operation. In this way, if the seasonal grade of the fuel available in the fuel tank does not correspond to the fuel grade mandated during the current season of vehicle operation, a fuel injection correction may be applied to compensate for differences in seasonal fuel grade.
In one example, prior to operation of a PHEV in the engine mode, a fuel age may be determined by the engine controller. The fuel age may be determined based on one or more of a distance traveled since the last refueling, an amount of fuel consumed since the last refueling, a fuel tank level, and season information from a real time clock or auxiliary system (e.g., navigation system) of the electric vehicle. Based on the age of the fuel and the current date, or season during which the vehicle is being operated, a seasonal grade of the fuel can be inferred (e.g., it may be determined whether the fuel is summer-grade or winter-grade fuel). Accordingly, an amount of fuel to be injected into the engine may be adjusted using a fuel correction factor that may compensate for differences in volatile compound composition and resultant fuel volatility of the fuel stored in the fuel tank relative to the fuel mandated at the current time of year, or season. In addition to the fuel injection amount, one or more other engine operating parameters may be adjusted using the fuel correction factor, such as engine boost, valve timing, throttle adjustments, etc.
In this way, by compensating for differences between the fuel currently available in the tank relative to the fuel currently sold (and mandated), exhaust emissions from the use of a winter-grade fuel during summer seasons may be brought closer to the exhaust emissions from the use of a summer-grade fuel. Additionally, engine cold starts during winter months using summer-grade fuel may be improved. As such, vehicle performance and emissions may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.